As communications technologies develop, a communications system becomes increasingly complex, and it is increasingly common that multiple receivers and transmitters in the communications system work simultaneously. A multiplexer is an important apparatus that enables multiple receivers and transmitters to work simultaneously by using a same antenna and is currently widely applied to many communications systems. For example, a duplexer is a three-port device, which is widely applied to an FDD (Frequency Division Duplexing) system.
Conventional multiplexers are all of a narrowband structure. A multiplexer designed based on a conventional structure is applicable only to a scenario with a relatively narrow bandwidth. Therefore, common multiplexers are mainly duplexers. Constrained by the structure itself, a higher-level multiplexer such as a triplexer, a quadplexer, or a quintuplexer, or a wideband multiplexer can hardly be designed based on the conventional structure. However, in the communications system, multiple wideband signals are often combined for transmission and/or receiving. Therefore, it is important to design a wideband multiplexer.